Give me some examples

I am getting a R9 280x Graphics card in my new PC.

Can someone tell me what kind of FPS I can expect to get in some high profile games, such as Skyrim, BF4, AC4, Etc. Also, on what Graphics Setting?

Also, may I ask what part of the PC determines how many mods can be run? I know it varies on what quality software but what software is it? I have a feeling it's on the CPU, I am getting an 8320, so should I be good?

By the way, although I do not know how at the moment, I plan to be overclocking.

I do not own a R9 280x, but if you Google and search "R9 290x [game] bencharmk", then there will probably be some information. As for mods, it uses everything in your system.